Photodynamic Therapy
(PDT or Blue Light Therapy)

Gary W. Cole, MD, FAAD

Dr. Cole is board certified in dermatology. He obtained his BA degree in bacteriology, his MA degree in microbiology, and his MD at the University of California, Los Angeles. He trained in dermatology at the University of Oregon, where he completed his residency.

William C. Shiel Jr., MD, FACP, FACR

Dr. Shiel received a Bachelor of Science degree with honors from the University of Notre Dame. There he was involved in research in radiation biology and received the Huisking Scholarship. After graduating from St. Louis University School of Medicine, he completed his Internal Medicine residency and Rheumatology fellowship at the University of California, Irvine. He is board-certified in Internal Medicine and Rheumatology.

What is photodynamic therapy (PDT)?

Photodynamic therapy (PDT) is a medical treatment that utilizes a photosensitizing molecule (frequently a drug that becomes activated by light exposure) and a light source to activate the applied drug. Very thin superficial skin cancers called actinic keratoses and certain other types of cancer cells can be eliminated this way. Acne can also be treated as well. The procedure is easily performed in a physician's office or outpatient setting.

PDT essentially has three steps. First, a light-sensitizing liquid, cream, or intravenous drug (photosensitizer) is applied or administered. Occasionally, a photosensitizing molecule that is already part of the body can be activated. Second, there is an incubation period of minutes to days. Finally, the target tissue is then exposed to a specific wavelength of light that then activates the photosensitizing medication.

Steps:

application of photosensitizer drug

incubation period

light activation

Although first used in the early 1900s, PDT in the modern sense is a new, evolving science. Current PDT involves a variety of incubation times for different the light-sensitizing drugs and a variety of light sources depending on the target tissue. The basic premise of PDT is selective tissue destruction.

At present, the primary limitation of available PDT techniques is the depth
of penetration of the light and ability to target cells within at most 1/3 of an
inch (approximately 1 cm) of the light source. Therefore, tumors or atypical
growths must be close to the surface of the skin or treatment surface for PDT to
work.

PDT is currently used in a number of
medical fields, including oncology (cancer), dermatology (skin), and cosmetic
surgery.

In dermatology, PDT with the photosensitizer Levulan Kerastick (20% delta-aminolevulinic acid HCl) is used for the treatment of very early, thin skin cancers called actinic keratoses (AK). The initial approval was specifically for the treatment of actinic keratosis of the face and scalp with a combination of an application of the photosensitizer followed by a timed exposure to a special blue light source. PDT is also used for acne, rosacea, skin cancer, sun
damage, cosmetic skin improvement, oily skin, enlarged sebaceous glands,
wrinkles, rejuvenation (anti-aging), warts, hidradenitis suppurativa, psoriasis,
and many other skin conditions. It is not used to remove moles or
birthmarks.